1. Field of the Invention
The present invention relates to a technology for transmitting a signal for a terrestrial digital broadcasting using synchronous optical network (SONET)/synchronous digital hierarchy (SDH) communication system.
2. Description of the Related Art
To improve image quality and to achieve advanced features in television, terrestrial digital broadcasting services are being offered. Specifically, terrestrial television broadcasting is digitalized, and then transmitted from towers on the ground (such as Tokyo Tower) to broadcast stations.
The mainstream method of transmitting signals of terrestrial digital broadcasting is the wireless signal transmission method (refer to “Digital Terrestrial Television Transmitter System in Tokyo Tower”, Tomohito Ikegami et al., NEC Giho Vol. 57, No.4/2004, pp. 49-54).
However, because wireless transmission is used for various purposes other than terrestrial digital broadcasting, many frequencies are competing with each other. Thus, there is a strong demand to transmit signals of terrestrial digital broadcasting by using fixed cables.
However, it is very difficult to transmit signals of terrestrial digital broadcasting by using fixed cables, because it entails many advanced specifications of interfaces between devices. Thus, none of the broadcast stations have realistic plans to implement cable signal transmission.
One approach is to build new cables dedicated for terrestrial digital broadcasting, connecting the broadcast stations. However, this is unfeasible because enormous costs are required.
It is therefore imperative to use existing general-purpose lines so that broadcast stations can realize cable signal transmission for terrestrial digital broadcasting without difficulty.